1. Field of the Invention
The present invention relates to a screw conveyor, and particularly to a screw conveyor comprising a propelling device to push plastic material such as butter, jam, and confectionery or bread dough, onto the screw of a screw conveyor.
2. Description of Prior Art
In conventional screw conveyors for plastic materials, the so-called bridge phenomenon, namely, as phenomenon where a mass of sticky material sticks to opposite walls, straddling screws and refuses to flow into them, frequently occurs. Further, plastic material is liable to adhere to walls of a hopper, thus obstructing the downward flow of the plastic material, resulting in the need for manually removing the obstacle.
U.S. Pat. No. 4,167,237 discloses a pressure feeder, including pusher assemblies where a hollow cylindrical pusher member, oval-shaped in cross-section, turns by a pinion gear to push a plastic material onto the screws of a screw feeder. Although this pusher member usually operates satisfactorily, it requires a fairly complex mechanism as it has a rack-and-pinion in a hollow cylindrical pusher member, which results in higher production costs. Further, the cylindrical pusher member requires a relatively large space. This is disadvantageous in that it necessitates overcoming a relatively large inertial resistance, and the screw feeder utilizing this cylindrical pusher member is inevitably large.